Power contactors are basically switching devices that are capable of closing and opening a circuit under substantial load currents. Diesel-electric locomotives traditionally use one or more power contactors to connect traction motors to a positive power bus. Typically, these contactors incorporate a device known as an arc chute to help dissipate the electric arc generated when the power contactor is opened while current is flowing through the power transmission circuit. Some modern locomotives incorporate a pulse-width modulation switching system, such as a chopper, in the primary current path of traction motor systems to more effectively regulate the operation of the traction motors. This pulse-width modulation switching system results in a discontinuous current at the power contactor. As a result, the power contactor, which was designed primarily for use in DC (non-pulsed) applications, is subjected to a pseudo-AC (pulsed) current.
One such example of a conventional power contactor is described in U.S. Pat. No. 3,992,599 (“the '599 patent”). The '599 patent purportedly discloses a contactor of high-current capacity that includes a blowout coil, which comprises a plurality of helical turns of a copper strap. The blowout coil surrounds a ferromagnetic core attached to the contactor by ferromagnetic flux-carrying pole pieces. As the blowout coil is within the primary current path, discontinuous current will induce current in the ferromagnetic core and flux-carrying pole pieces.
Conventional power contactors that include a coil surrounded by a ferromagnetic core, such as the one described in the '599 patent, have significant drawbacks, particularly when used in applications that require discontinuous or “pulsed” current. In particular, induction caused by the frequent, periodic change in pulsed or discontinuous current results in overheating of metallic contactor components not in the primary current path, including the ferromagnetic core, the bolt assembly, and any other metallic material, such as side plates. Such heating can be extreme, particularly in locomotive applications, where current is high and pulse width tends to be fairly short. If allowed to persist, extreme temperatures can potentially result in catastrophic failure of the materials, which can lead to malfunction of the power contactor. Because proper operation of the power contactor is critical to maintaining operation of the traction motor, the effects of excessive temperatures in the power contactor components due to the induction caused by pulsed or discontinuous currents must be mitigated.
The presently disclosed locomotive power contactor is directed to overcoming one or more of the problems set forth above and/or other problems in the art.